In (parametric) spatial audio (en)coders, parameters are extracted from the original audio signals so as to produce a reduced number of down-mix audio signals (for example only a single down-mix signal corresponding to a mono, or two down-mix signals for a stereo down mix), and a corresponding set of parameters describing the spatial properties of the original audio signal. In (parametric) spatial audio decoders, the spatial properties described by the transmitted spatial parameters are used to recreate a spatial multi-channel signal, which closely resembles the original multi-channel audio signal.
Recently, techniques for processing and manipulating of individual audio objects at the decoding side have attracted significant interest. For example, within the MPEG framework, a workgroup has been started on object-based spatial audio coding. The aim of this workgroup is to “explore new technology and reuse of current MPEG Surround components and technologies for the bit rate efficient coding of multiple sound sources or objects into a number of down-mix channels and corresponding spatial parameters”. In other words, the aim is to encode multiple audio objects in a limited set of down-mix channels with corresponding parameters. At the decoder side, users interact with the content for example by repositioning the individual objects.
Such interaction with the content is easily realized in object-oriented decoders. It is then realized by including a rendering that follows the decoding. Said rendering is combined with the decoding to prevent the need of determining individual objects. The currently available dedicated rendering comprises positioning of objects, volume adjusting, or equalization of the rendered audio signals.
One disadvantage of the known object-oriented decoders with the incorporated rendering is that they permit a limited set of manipulations of objects, because they do not produce or operate on the individual objects. On the other hand explicit decoding of the individual audio objects is very costly and inefficient.